Single beam quantitative phase contrast 3D microscopy of cells

Imaging of cells is an interesting and challenging problem as they do not appreciably change the amplitude of the electromagnetic radiation interacting with them. Phase contrast techniques can be used to overcome this hurdle. Interferometric phase contrast techniques like digital holography can be used for quantitative phase contrast microscopic imaging of transparent objects and it yields the three dimensional profile of the object under investigation. These methods also have advantage of numerical focusing, allowing one to focus on to any desired object plane. But most of the interferometric quantitative phase contrast techniques require two beams as well as the adjustment of the beams for high fringe contrast, requiring stringent optical conditions. Here we present a single beam phase retrieval technique for quantitative phase contrast microscopy of cells. The phase information of the object is obtained by sampling the volume speckle field generated by the object at several axial planes. These intensity patterns are used iteratively in the diffraction integral to retrieve the phase information about the object. The advantages of this technique include compactness, immunity to external vibrations as well as the prospect of usage of low coherent sources.